1. Field of the Invention
The subject invention generally pertains to industrial rollup doors and more specifically to a flexible curtain that can replace a lower section of such a door.
2. Description of Related Art
Roll-up doors typically comprise a flexible roll-up panel or curtain that is wound about an overhead roller. Roll-up curtains can be made of pliable fabric or a series of pivotally interconnected, horizontal rigid slats made of metal or some other rigid material. To close the door, the roller pays out the curtain as two vertical tracks disposed along either side edge of the doorway guide the side edges of the curtain along a generally vertical plane across the doorway. The rotation of the roller is reversed to open the door. Typically, roll-up doors are either powered open and closed or are powered open and allowed to descend by gravity.
Fabric curtains are generally lightweight and pliable, which typically makes them faster operating and more impactable than metal roll-up curtains. In some applications, fabric curtains are reinforced with a series of relatively stiff horizontal stays or windbars, which help prevent the curtain from billowing due to air pressure differentials across opposite faces of the curtain.
Metal curtains, on the other hand, are usually heavier and slower, but their horizontal rigidity and strength make them particularly suitable for use on exterior roll-up doors where security and wind resistance is important.
Metal roll-up doors, unfortunately, are generally less impactable than fabric doors. A forklift, for instance, may accidentally strike a roll-up door and force its curtain out from within the door's vertical guide tracks. If the curtain is made of a pliable fabric, the curtain may be readily reinserted into the tracks and the door returned to normal operation without any permanent damage. If the door has a curtain comprised of rigid metal slats, however, an impact can permanently bend or damage several of the slats. It seems that the slats near the lower edge of the curtain are the ones that are most often damaged due to forklifts or other vehicles attempting to pass through the doorway when door is not completely open. Sometimes just a few of the lowermost slats are damaged, but much higher slats can also be affected.
In some cases, the lowermost slats of a metal door can be replaced by a product known as a MATADOOR curtain, which is made by Cornell Iron Works of Mountaintop PA. A Matadoor curtain is a breakaway pliable curtain section that can be attached to the lower edge of the remaining undamaged upper section of a metal curtain. Although such a product may be effective, it does have its limitations.
First, the bottom bar of such a curtain assembly has a riveted connector that can break away in response to an impact. After breaking away, the bottom bar apparently needs to be repaired by using a tool to rivet or otherwise reassembly the connector and the bottom bar back together
Second, the width of doorways may vary widely, which raises the question of where to place the breakaway connector. If the connector belongs at the center of the doorway, the two bottom bar segments may both need to be custom cut to fit. Since the two bottom bar segments are not identical due to their beveled edges at the central connector, both right-hand and left-hand bar segments may need to be stocked for ensuring ready availability.
Third, although conceivably any size fabric sheet could be cut to match the opening left by the removed damaged slats, a final curtain assembly is not so readily made to just any size. A single roll of curtain material may have to be unreasonably large and cumbersome for it to be sufficiently large to cover any possible height and width.
Fourth, the height of this type of replacement curtain may vary depending on how many slats are being replaced. If the height becomes too great, the curtain may tend to billow for its failure to provide any means for installing windbars.
Fifth, a tall section of fabric curtain may be appreciably lighter than the metal slats it is replacing. Since a roll-up door's counterweight spring is presumably preloaded to match the metal curtain's original weight, the spring preload may be too great for a curtain whose weight has just been reduced due to the installation of a sizable fabric curtain section. Thus, replacing metal slats with such a curtain may involve having to adjust the preload of the door's counterweight spring.
Consequently, a need still remains for a quick and effective way of replacing the damaged bottom section of a metal roll-up door whose damaged section is of an indeterminate size.